Help on decorating the chairs for weddng?

All I could find to rent for my wedding this summer are white metal folding chairs with white seats. I’ve not seen the chairs, I don’t know if I will before the wedding since I’m renting them from out of town. I’m buying some 1.5" wide ribbon and plan on just wrapping the top of each chair just once and then attaching some decoration on the back where the ends of the ribbon will meet. The ribbon is white, pink and green stripes. Any ideas on how much ribbon per chair would be needed, I’m guessing for an average size folding chair, and what to put for the decoration on the back? Links would be helpful too! Oh and it will be an outdoor wedding next to a waterfall. Thanks!